Twenty-six unembalmed lower-leg specimens were mounted in an experimental test device with the foot placed at a fixed degree of pronation/supination, dorsiflexion/plantar flexion, or both. Torque versus rotation curves were determined as each foot was externally rotated to failure. Torsional stiffness was determined for the first 20° of external rotation, and energy to failure was noted at the point of initial failure. Anatomic dissection and roentgenographs delineated the degree of injury in all specimens. Gender had the greatest effect on both torque and energy parameters, and the injury pattern. In males, 67% of specimens had an oblique fibular fracture, torn anterior tibiofibular ligament, and torn deltoid ligament (SER2). In females, 45% had a transverse fibular fracture without syndesmotic or deltoid injury. Forty percent of females had the SER2 injury. Angle of supination/pronation did not correlate with a specific injury pattern. Peak axial load had a significant effect on stiffness, but increasing the load by more than three times body weight did not increase injury severity.